Electrocoagulation is the process of destabilizing suspended, emulsified, or dissolved contaminants in an aqueous medium by introducing an electrical current into the medium. The electrical current provides an electromotive force to drive the contaminants out of suspension, emulsion, or solution and produce solids. The contaminant solids form hydrophobic entities that precipitate and are easily removed by any number of secondary separation techniques, such as, by way of non-limiting example, electrolytic flotation to remove coalesced colloidal materials.
Electrocoagulation systems are capable of removing a diverse array of contaminants, including, by way of non-limiting example, paper pulp mill waste, metal plating waste, tannery waste, cannery waste, steel mill effluent, slaughterhouse waste, chromates, lead species, mercury species, and domestic sewage. The wastewaters containing these and other contaminants are generally reduced to water that is substantially clear, clean, and odorless, and thus capable of reuse in various applications.
However, previous electrocoagulation water treatment systems are not capable of removing certain contaminants to below safe or legal limits from certain input streams. One contaminant in particular that is difficult to remove by electrocoagulation is ammonia and related species, which may make up a substantial proportion of the contaminants in, by way of non-limiting example, municipal sewage streams. Although some attempts have been made to provide for electrocoagulation systems that remove ammonia, these have typically suffered from a number of drawbacks. For example, U.S. Patent Application Publication 2014/0021057, published 23 Jan. 2014 to Berrak (“Berrak”), discloses electrocoagulation methods for the removal of ammonia, but the methods of Berrak are not capable of providing treated streams with ammonia contents lower than about 13 mg/L and require a relatively narrow pH range for the input stream. As a result, prior art water treatment systems utilizing electrocoagulation must be provided in conjunction with one or both of pretreatment (to provide an appropriate input pH) or posttreatment (to further remove ammonia) by other methods to provide treated streams with acceptable ammonia content.
Another general contaminant of concern includes certain nitrogen compounds. Increased levels of nitrates are a potential health hazard for drinking water when ammonia fertilizer is applied to farmland. Centrate from municipal sewer plants are a major loading source for nitrogen contaminants when the centrate is returned to the front of the plant for further processing. Achieving nitrogen compliance levels is becoming more difficult for sewage plants as governmental regulations limits are lowered.
There is thus a need in the art to provide efficient systems for treating aqueous wastes by electrocoagulation that reduce an ammonia content of the aqueous waste to acceptable levels, and that are capable of operation over a wide range of input pH. There is also a need to remove sufficient levels of nitrogen contaminants.